Mathematics – Logic
Scientific paper
Feb 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989gecoa..53..269s&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 53, Issue 2, pp.269-278
Mathematics
Logic
35
Scientific paper
The solubility of gold was measured in aqueous sulfide solutions at pH from 3 to 8, 150° to 350°C, and at pressures determined by the liquid-vapor pressure of the solution, with oxidation state fixed or buffered by either sulfate-sulfide equilbria or H 2 (g). High solubilities were measured in solutions with near neutral pH with a maximum measured gold concentration of 0.036 m (7224 mg/kg) at 350°C in a solution containing 0.66 m H 2 S and 0.28 m NaHS. The results are consistent with the aqueous complex Au(HS) 2 - . Log equilibrium constants for the reaction at 150°, 200°, 250°, 300°, and 350°C were determined as -2.39 ± 0.2, -1.89 ± 0.2, -1.56 ± 0.3, -1.35 ± 0.3, and -1.22 ± 0.2, respectively. These values are in reasonable agreement with published data at both 25°C and elevated temperatures. The high stability of Au(HS) 2 - indicates that geologically significant quantities of gold can be transported in typical hydrothermal solutions. Calculated gold solubility for the Ohaaki geothermal system in New Zealand shows that Au(HS) 2 - can easily account for the measured hydrothermal gold concentration. Gold may be precipitated from solution by both pH and redox changes. In addition, decreasing the activity of sulfide in solution is an effective mechanism for gold deposition. Analysis of the effect of temperature on the solubility of gold shows that a decrease in temperature may increase or decrease solubility. Deposition by cooling depends upon the pH-oxidation state path of the solutions.
Barnes Hubert L.
Shenberger D. M.
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